Joint scaling test to estimate genetic parameters of soybean resistance to frogeye leaf spot

To study the inheritance of soybean resistance to Cercospora sojina Hara, genetic parameters were estimated using means and variances of populations derived from a cross between a resistant and a susceptible cultivar, namely, ‘Uberaba’ and ‘Bossier’, respectively. The parents and the F 1 , F 2 , BC 1 and BC 2 generations were evaluated for six characteristics associated with the disease: visually evaluated infection degree; number of lesions per leaflet; lesion mean diameter; percentage of lesioned leaf area, number of lesions per square centimeter and disease index. The additive genetic effect was the most important in the determination of all traits related to soybean resistance to frogeye leaf spot. The infection degree, a subjective trait that considers the set of all resistance related characteristics in its constitution, presented positive variance and lower influence of the environment, consisting in a useful variable in programs of soybean breeding aiming at the resistance to C. sojina. All traits presented at least one type (aa, ad or dd) of significant epistatic interaction and the full model (additive + dominant + epistatic) was more adequate to describe the resistance.